1. Field of the Invention
The present invention relates to a method of tracking a resolved component of a multi-path signal assigned to a rake finger of a spread spectrum rake receiver, more particularly to such a rake receiver included in a spread spectrum communication device such as a CDMA handset.
2. Description of the Related Art
Cellular communication systems are well-known. Such cellular communication systems comprise cells or radio zones, together covering a given geographical area. The cells include base stations that, through control and communication channels, establish and maintain communication links with mobile communication devices that are comprised in the system, and communicate with the mobile communication devices through established communication links.
One type of a cellular communication system is a so-called Direct Sequence CDMA (Code Division Multiple Access) spread spectrum system. In such a CDMA spread spectrum system, in addition to a transmitter, the mobile communication device typically has a so-called rake receiver with a number of rake fingers to resolve components of a multi-path received spread spectrum signal and to diversity combine resolved components so as to improve the signal-to-noise ratio of the received signal. The spread spectrum signals are received from transmitters that spread data signals over a frequency band by using spreading sequences. Elements in such a sequence are so-called chips. For spreading different data signals at different transmitters Walsh sequences are used for channelization and pseudo-noise-spreading sequences are used for scrambling. The rake receiver regenerates a data signal from a received spread spectrum signal by de-scrambling it with the same pseudo-noise sequence and by de-spreading it thereafter with the same Walsh sequence that was used to spread the data signal, and diversity combines multi-path received signals that originate from the same data signal. The rake receiver needs to initially synchronize to the transmitter from which it wants to receive a data signal. During such initial synchronization, a searcher comprised in the rake receiver resolves components of a multi-path received signal, the components originating from the wanted data signal. Thereafter, the rake receiver adopts a tracking mode synchronization to keep the rake fingers synchronized to the resolved components that originate from the same wanted data signal. During tracking mode synchronization the rake fingers are kept aligned with their resolved components.